Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known airfoil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
Modern utility-grade wind turbines generally include redundant braking systems. An aerodynamic braking system slows or stops rotation of the rotor blades by pitching the blades to a feathered position. Such systems may include a stored energy source to enable the rotor blades to be pitched during a power failure. A mechanical braking system, such as a hydraulic brake, is also generally provided to stop the rotor against full wind speed. A stored energy source, such as a hydraulic accumulator, may enable actuation of the mechanical brake during a power failure.
Extreme loads are generated on various wind turbine components at rotor overspeed conditions, particularly at overspeed fault conditions, and it is thus an important operating consideration to maintain tight control over the rotor speed. The fault loads on the rotor blades, hub, and main shaft are typically the design driving loads for these components. Under traditional braking control methods, aerodynamic braking is utilized at rotor speeds in excess of nominal rotor speed and the mechanical brake is applied after the turbine faults at a defined rotor speed, which is typically at about 111%. The mechanical brake is activated in accordance with a time-dependent braking profile. However, with this control methodology, the extreme transient loads experienced at the fault speed are not significantly eliminated.
Accordingly, an improved system and/or method for braking the wind turbine rotor at overspeed conditions would be welcomed in the technology.